Sound/Transcript
Transcript Text Reads: THE MYSTERIES OF LIFE WITH TIM & MOBY TIM: Dear Tim & Moby, What is sound? From Nathanlo. An animation shows a hand holding a letter. The letter indicates Nathanlo is from Plano. TIM: Cut it out! An animation shows Tim standing next to Moby holding a hammer in his hand and banging on his head with it. TIM: Sound travels in waves, like the ones in the ocean. Well, not exactly the same. Ocean waves vibrate up and down at a right angle to the direction of the wave. That's called a transverse wave. An animation shows the ocean waves moving right to left across the screen. TIM: Sound travels in something called a longitudinal wave. Here, we'll show you. An animation shows a sound wave represented by a series of arcs moving left to right across the screen. Each arc is nearly a vertical line segment, with some curvature to the left, so that each curve appears to be moving directly away from its center. The arcs are spaced evenly in the horizontal direction. TIM: A sound wave is a chain of vibrating molecules. Hitting these cymbals causes air molecules to vibrate. An animation shows Tim sitting at a drum set and holding drum sticks. Moby is holding an electric guitar, which he strums once. TIM: The vibration pushes nearby air molecules back and forth, making the local air pressure rise and fall. In the animation, a close up of the edge of one of the cymbals is shown. The cymbal is struck by a drumstick with an audible crashing sound. After it is struck, the cymbal vibrates up and down. Sound waves, represented by a series of arcs, move up from the surface of the cymbal and out of view in an upwards diagonal direction. This repeats several times. TIM: Let's see it in slow motion. MOBY: Beep. TIM: As the cymbal pushes into the air, air molecules are packed tighter, creating a compression. An animation shows the cymbal causing compression of the air. Air molecules, represented by blue spheres, are arranged randomly throughout the space above the surface of the cymbal. As the cymbal moves up, it pushes some of the air molecules up with it, causing an increase in the density of air molecules in the space directly above. TIM: When the cymbal pulls back in its vibration, it creates a low pressure area called a rarefaction. The animation continues, showing the cymbal moving back down. The air molecules spread into the available space until they are arranged similarly to the beginning of the compression cycle. TIM: Put 'em together, and you get a cycle, and these cycles form a longitudinal wave. Humans can hear sounds from 20 to 20000 cycles per second. An animation shows a sound wave diagram consisting of a long succession of arcs moving right to left behind Tim's head. TIM: This oscilloscope is designed to measure sound waves. How loud a sound is depends on the force of the compression, or the amplitude. A low amplitude produces a quiet sound, and high amplitude means loud noise! An animation shows an oscilloscope. The oscilloscope is a dark screen with a bright trace, or path, extending across the width of the screen. The trace begins as a flat, horizontal line. As “amplitude” is mentioned, a representation of a low amplitude sound wave is shown. At the same time, the oscilloscope trace becomes a curved path, wiggling up and down across the width of the screen, forming a wave-like shape. The trace wiggles up and down a little more than twice within the width of the screen. The up and down wiggles fill about one third of the screen height. When Tim describes high amplitude, a representation of high amplitude sound waves appears below the low amplitude waves. At the same time, the oscilloscope trace changes to showing the high amplitude wave. On the oscilloscope, the trace of the high amplitude wave is still an up-and-down wiggling path, but now the up and down wiggles nearly fill the vertical space on the screen. TIM: The pitch of a sound comes from the wave's frequency. In the animation, the sound waves disappear, and the oscilloscope trace is flat again. TIM: High frequency waves make high-pitched sounds. In the animation, a representation of high frequency sound waves appears in the middle of the screen. This representation has a series of arcs whose spacing varies periodically. The representation appears three times. The oscilloscope trace becomes a wiggled path again, with about eight up and down wiggles on the screen. A high-pitched tone is heard. TIM: Low frequency waves make low-pitched sounds. In the animation, a representation of low frequency sound waves appears above the high frequency sound. This representation has a series of arcs whose spacing varies periodically. The representation appears slightly more than once. The wiggles on the oscilloscope spread out so that the trace only goes up and down once within the width of the screen. A low-pitched tone is heard. TIM: Usually, all sounds travel through the air at 344 meters per second. If it's warmer, the sound can travel faster. Colder air makes sound slower. An animation shows Moby holding a guitar and standing next to Tim. Moby strums the guitar. Another animation shows a radio emitting sound waves. In the background, the screen is split horizontally, with a desert scene on the left and a snow-covered landscape on the right. Waves moving left into desert scene are moving faster than waves moving right into the snowy scene. TIM: Sound can travel 1524 meters per second underwater and around 5486 meters per second through steel. An animation shows a cluster of sound waves passing by a fish in the water. Another animation shows Tim pressing his ear down onto a railroad track. The sound of a train can be heard in the background while Tim is speaking. TIM: Sound can travel a whole lot further through denser mediums. Whales can communicate with each other by making sounds that travel thousands of miles. An animation shows the head of a blue whale. A low, groaning sound can be heard. Text Reads: "Hey, Dan's having a party on Tuesday." Another low, groaning sound is heard. Text reads: "Cool. I'll be there." TIM: Sounds can be reflected or absorbed by things that they hit. An echo is sound that bounces off hard, smooth surfaces back to your ears. An animation shows Tim standing in front of a rocky cliff. TIM: Hello! A series of fading echoes of the "Hello!" are heard. TIM: Hello! An animation shows Tim standing next to a bed and shouting toward the pillow. TIM: Soft surfaces like grass or pillows will absorb sound waves. An animation shows Moby holding a guitar and standing next to Tim. Moby strums the guitar. TIM: You only know one chord, don't you? In the animation, Moby strums the guitar again. Category:BrainPOP Transcripts